1. Field of the Invention
The present invention is directed to wellbore overshots and, in one particular aspect, to overshots for tubing. In one specific embodiment the present invention is directed to an overshot for engaging and retrieving collapsed coiled tubing.
2. Description of Related Art
The prior art discloses a wide variety of wellbore overshots for engaging and retrieving tubulars and other "fish" used in a wellbore. Often in using coiled tubing, the tubing collapses. There has long been a need for an overshot useful in a wellbore to effectively engage and retrieve collapsed coiled tubing.
FIG. 1 shows a prior art overshot 10 with an outer cover sleeve 20, a mandrel 30 disposed substantially within the cover sleeve 20, and a body member 40 disposed within the cover sleeve 20 opposite the mandrel 30. One or more set screws 21 secures the mandrel 30 within the cover sleeve 20. A lower end 22 of the cover sleeve 20 projects down below a lower end 31 of the mandrel 30 and a lower end 41 of the body member 40. Preferably the lower end 22 of the cover sleeve is sized and disposed for encompassing a top of collapsed coiled tubing or of a fish. A top end 32 of the mandrel 30 has a threaded portion for releasably connecting the overshot to a work string. The body member 40 has an upper shoulder 42 that abuts a lower shoulder 33 of the mandrel 30. An alignment pin 11 extends through the body member 40 and the mandrel 30. A plurality of slips 60 are each movably disposed in a corresponding slip channel 43 of the body member 40. A spring 61 biases each slip downwardly. A portion of each spring 61 extends through a spring channel 63 in each slip body 62. The mandrel 30 has an inner wall 35 with upwardly directed teeth 36. Each slip 60 has an outer surface 64 with upwardly directed teeth 65. The inner wall 35 of the mandrel 30 and an inner wall 45 of the body member 40 define a space S into which part of a fish or coiled tubing may project for gripping between the mandrel 30 and the slips 60. Each slip 60 has a lower inclined surface 66 which corresponds to and rides on a lower inclined surface 46 of each slip channel 43 of the body member 40. Each slip 60 has an upper inclined surface 68 which corresponds to and rides against an upper inclined surface 48 of the slip channels 43. Each slip 60 has a lower inclined surface 80 against which a fish or tubing may push or be pushed to push the slip up in its slip channel thereby permitting the fish or tubing to enter into the space S between a slip and the inner wall of the mandrel so that the fish or tubing may be gripped therebetween. The slips are sized so that they cannot exit their slip channels into the space S and cannot fall out of the overshot. A shoulder 69 of each slip abuts a shoulder 49 of the body member to prevent further upward slip movement. A pointed end 37 of the mandrel 30 and a pointed end 47 of the body member 40 facilitate reception of a fish or tubing within the overshot and movement of the fish or tubing into the space S.